SfePy December 2016

sfepy@python.org

5 participants
11 discussions

Calculate total force from cauchy stress

by Patricia Garcia Cañadilla

Dear Robert, I have a 2D body of hyperelastic material which contracts and I would like to compute the total force developed by the body from the cauchy stress. I am trying to follow some of your indications I found in this group, but I still couldn't make it works. Could you please help me to fix the problem? I am getting the following error: key = (region.name, integral.order, integration) AttributeError: 'dict' object has no attribute 'name' I am trying to do the following, inside stress_strain post-processing function: def stress_strain(out, problem, state, extend = False ): from sfepy.base.base import Struct from sfepy.mechanics.tensors import StressTransform from sfepy.mechanics.tensors import transform_data from sfepy.discrete.common.mappings import get_normals ev = problem.evaluate field = problem.fields['displacement'] region = problem.domain.regions['Gamma'] integral = problem.integrals['i2'] n = get_normals(field,integral,regions) stress = ev('dw_tl_fib_a.1.Omega(f1.fmax, f1.eps_opt, f1.s, f1.fdir, f1.act, v, u )',mode='qp', term_mode= 'stress'); F = ev('ev_def_grad.1.Omega(u)',mode='el_avg'); transform = StressTransform(F) Cstress = transform.get_cauchy_from_2pk(stress) T = Cstress*n; Force = ev('ev_surface_integrate.2.Gamma(T)') And here it is part of the problem configuration file. fields = { 'displacement': ('real', 'vector', 'Omega', 1), } materials = { 'solid' : (None, 'get_elastic_pars'), 'load' : (None, 'linear_tension'), 'f1' : 'get_pars_fibres1', } variables = { 'u': ('unknown field', 'displacement', 0), 'v': ('test field', 'displacement', 'u'), } regions = { 'Omega' : 'all', 'Fix1' : ('vertices in x < %.10f' % (fix_point + eps2), 'facet'), 'Fix2' : ('vertices in x > %.10f' % (fix_point - eps2), 'facet'), 'Fix' : ('r.Fix1 *v r.Fix2', 'facet'), 'Gamma' : ('vertices of surface','edge'), } ebcs = { 'fixb' : ('Fix', {'u.all' : 0.0}), } integrals = { 'i1' : ('v', 1), 'i2' : ('s', 2), }

2 years, 1 month

Re: Torque

by Robert Cimrman

In examples/large_deformation/hyperelastic.py a rotation by displacements is applied. By using a similar function the vectors defining the force couples could be defined for dw_surface_ltr (IMHO). Does it make sense? r. ----- Reply message ----- From: "Andre Smit" <freev...(a)gmail.com> To: <sfepy...(a)googlegroups.com> Subject: Torque Date: Sat, Dec 18, 2010 05:10 What is the best way to apply a torque load to a model? -- Andre -- You received this message because you are subscribed to the Google Groups "sfepy-devel" group. To post to this group, send email to sfepy...(a)googlegroups.com. To unsubscribe from this group, send email to sfepy-devel...(a)googlegroups.com. For more options, visit this group at http://groups.google.com/group/sfepy-devel?hl=en.

2 years, 12 months

new interactive example with time stepping

by Robert Cimrman

Hi, I have just updated the time stepping solvers in sfepy for interactive use, as demonstrated in the new example [1]. For basic use, ignore the probing code - the time stepper can be used as simply as: tss = SimpleTimeSteppingSolver({'t0' : 0.0, 't1' : 100.0, 'n_step' : 11}, problem=problem) tss.init_time() for step, time, state in tss(): pass r. [1] http://sfepy.org/doc-devel/examples/diffusion/time_poisson_interactive.html

3 years, 11 months

one problem in ''biot.py"

by Kid Guo

Hi, I have a problem based on "../sfepy/examples/multi_physics/biot.py". In the attached scripy 'block2.py', I have calculated the stress and strain according to the displacement, at the 111 and 112 lines you can see it. Now I want to output the K of every cell, I gave a value of k at the 64 line in this script, it is a 3*3 array. I don't know which function or equation to use, so I was stucked at the 113 line. if I change the K value, will where be some difference results? Thank you advance K.

4 years, 1 month

Correct unit in linear volume force term

by Radko Bankras

Hi, My mesh is defined in mm. With units = ['mm', 's', 'kg', 'C'] the matching units for density and force are Tg/m**3 and mNewton, respectively. I would like to determine the linear elastic displacement of the meshed object by gravity, using the linear volume force term t2 = Term.new('dw_volume_lvf(f.val, v)', integral, omega, f=f, v=v) in which the force vector f.val is obtained from function get_gravity. def get_gravity(ts, coors, mode=None, equations=None, term=None, problem=None, **kwargs): if mode == 'qp': # define material parameters in quadrature points fx = nm.zeros((coors.shape[0], 1, 1)) fy = nm.zeros((coors.shape[0], 1, 1)) fz = nm.tile(-2.285e-2, (coors.shape[0], 1, 1)) # constant vertical force in mN/mm3 val = nm.concatenate((fx, fy, fz), axis=1) # concatenate force components return {'val': val} With gravity g = 9.81 m/s**2 and density rho = 2.329e-6 Tg/m**3, the constant volume force 2.285e-2 mNewton/mm**3 is obtained as the product of gravity and density. Is it correct that f.val in the linear volume force term is defined in force per unit volume? And another newbie question: Is it correct that a first order integral is used for the linear volume force term, because of the linear relation between force and volume? Or is a higher integral order needed, due to the dimensions of the mesh? Kind regards, Radko

4 years, 2 months

Vector decomposition of ev_cauchy_strain

by Radko Bankras

Hi, The following code is used in example linear_elasticity/material_nonlinearity.py to evaluate the Cauchy strain during post processing: strain = problem.evaluate('ev_cauchy_strain.i.Omega(u)', mode='el_avg') out['cauchy_strain'] = Struct(name='output_data', mode='cell', data=strain, dofs=None) Using ParaView to visualize the result on a tetrahedral mesh from VTK output, I find the strain to have 8 decomposition components with arbitrary names 1 through 8. Is it possible to obtain the strain as a vector in Cartesian components? Regards, Radko

4 years, 2 months

Passing function values in interactive mode

by David Jessop

Hi, I'm trying to solve a non-linear Poisson type equation where the diffusion coefficient/conductivity depends on the field variable. Logically, I've tried basing this part of my code on the poisson_field_dependent_material.py case and, of course, it works nicely in "simple" mode but I can't figure out how to pass the value to my material variable "cond" in interactive mode (I require interactive mode for reasons stated in this post <https://groups.google.com/forum/#!topic/sfepy-devel/es64x4YFEiU>). I define the same get_conductivity function as per poisson_field_dependent_material.py, then declare the function as conductivity_fun = Function('conductivity_fun', get_conductivity) get_conductivity returns a dictionary key/value pair {'val' : val} so I figured to call the function as per cond = Material('cond', conductivity_fun) should work, but it results in this error: Traceback (most recent call last): File "examples/diffusion/myPoisson/myPoissonInteractive.py", line 185, in <module> main() File "examples/diffusion/myPoisson/myPoissonInteractive.py", line 116, in main cond = Material('cond', conductivity_fun,) #val= 2.0) File "/usr/local/lib/python2.7/dist-packages/sfepy-2016.3_git_94dff5a051dbd2bf6bd56fce936d75878edef9e8-py2.7-linux-x86_64.egg/sfepy/discrete/materials.py" , line 148, in __init__ % self.name TypeError: not enough arguments for format string I've also tried passing a function handle to cond ('conductivity_fun'), and all the possible combinations of function names that I can think of, but this error persists. I've looked at the function documentation <http://sfepy.org/doc-devel/users_guide.html#functions> but unfortunately this hasn't clarified things for me as this issue pertains specifically to the interactive problem specification. Thank you for your help. Regards, David

4 years, 2 months

specifying an initial guess for non-linear problems with no ebcs

by David Jessop

<https://lh3.googleusercontent.com/-nqPKBodss14/WEbGCb-rgXI/AAAAAAAAA70/sQ8d…> Hi, I have a non-linear form of the Poisson equation where the "diffusion" coefficient depends on the derivatives of the state variable (see image). There are no Dirichlet-type boundary conditions (i.e. no ebcs) so I really need to specify a good initial guess at the solution. My questions are: 1) How are initial guesses passed to the solver? From the documentation, it doesn't seem like initial guesses can be directly passed to the nls.newton solver as an argument (though they are an argument of the subroutine __call__). 2) In what form should the initial guess vector/array be written? Can a function be passed? Do numerical values have be be specified at the mesh nodes? Thanks for any help on this matter. D

4 years, 2 months

errors when running ipython --profile=sfepy

by silesa...＠hotmail.com

Hello, I have created an ipython profile for sfepy, i have edited the file ~/.ipython/profile_sfepy/ipython_config.py addinging the suggested lines in the installation manual. My system is Fedora 24 Igot the following errors: IPython profile: sfepy --------------------------------------------------------------------------- ImportError Traceback (most recent call last) <ipython-input-1-3df2942fcc0c> in <module>() ----> 1 from sfepy.base.base import * ImportError: No module named sfepy.base.base --------------------------------------------------------------------------- ImportError Traceback (most recent call last) <ipython-input-1-7107ce501ecc> in <module>() ----> 1 from sfepy.discrete import * ImportError: No module named sfepy.discrete --------------------------------------------------------------------------- ImportError Traceback (most recent call last) <ipython-input-1-4cb6370fc83c> in <module>() ----> 1 from sfepy.discrete.fem import * ImportError: No module named sfepy.discrete.fem --------------------------------------------------------------------------- ImportError Traceback (most recent call last) <ipython-input-1-774ff483fc4b> in <module>() ----> 1 from sfepy.applications import solve_pde ImportError: No module named sfepy.applications Is it possible to correct those errors? I'll appreciate any help. Hugo

4 years, 2 months

error while running poisson_short_syntax.py

by silesa...＠hotmail.com

Hello every body, I just have installed in place Sfepy-2015.4 on fedora 24, seems that every thing went fine during the installation, but when I run the tests, more than 50 test failed, in particular when I run the examples/diffusion/poisson_short_suntax.py I got the following last message: File "/usr/lib/python2.7/site-packages/scikits/umfpack/_umfpack.py", line 776, in umfpack_dl_symbolic return __umfpack.umfpack_dl_symbolic(n_row, n_col, Ap, Ai, Ax, Control, Info) TypeError: in method 'umfpack_dl_symbolic', argument 1 of type 'SuiteSparse_long' I really will appreciate any help Hugo

4 years, 2 months

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SfePy December 2016